This invention relates to a process for the preparation of organic fluoride compounds, and in particular, to a process for the liquid phase replacement of halogen atoms with fluorine in organic compounds.
A variety of fluorination processes are known wherein fluorine replaces one or more halogen substituents of a halogenated organic compound. Such known processes include both vapor phase fluorination reaction and liquid phase fluorination reactions. Typically, such processes involve the reaction of a halocarbon compound with a fluorination agent, sometimes in the presence of catalyst, such as antimony pentachloride, at atmospheric or super-atmospheric pressures. Many of the known processes, while suitable for laboratory investigations and experiments, are unsuitable for commercial use for various reasons, such as the low purity or yield of product, the need for containment of high pressures, the high cost of equipment which must be employed, or the need for frequent replacement of the catalyst, due to loss or deactivation. One of the common difficulties encountered in vapor phase fluorination reactions results from the highly exothermic nature of such reactions. The heat evolved frequently results in a temperature rise sufficient to cause thermal decomposition of some of the organic starting materials and a resultant carbonization of the catalyst. Furthermore, such vapor phase reactions commonly require the use of substantial stoichiometric excess of hydrogen fluoride with the attendant problem of disposal of the hazardous hydrogen fluoride containing effluent gases.
Some of the problems associated with vapor phase fluorination processes may be avoided through the use of liquid phase fluorination. However, although atmospheric liquid phase fluorination processes are known and are used in laboratory preparations, they have not received widespread acceptance for larger scale commercial use for various reasons. Heretofore, the most widely used catalyst for liquid phase fluorinations has been antimony pentachloride or a mixture of antimony pentachloride and antimony trichloride. However, antimony chlorides, although highly effective in the catalysis of many fluorination reactions, are very volatile materials. To avoid the problems associated with the volatility of antimony chlorides, such fluorination reactions are often carried out in closed systems under super-atmospheric pressure, necessiating the use of pressure equipment. In addition it has been found that to obtain desirably high yields, antimony chloride catalysts must be employed in relatively large concentrations. Thus, although antimony chlorides provide an effective catalyst for many fluorination reactions, a need exists for a still more effective catalyst that will overcome the aforementioned disadvantages.
A wide variety of other fluorination catalysts are known and have been used for various fluorination processes. However, the efficacy of a particular catalyst is highly specific and may depend on the nature of the reactants, that is the specific compound to be fluorinated and the particular fluorinating agent employed as well as the condition of the fluorination reaction, such as temperature, pressure, and physical phase of reactants.
It is an object of the present invention to provide an improved process for the liquid phase fluorination of organic halides. It is a further object to provide an improved catalyst for fluorination reactions that is relatively low in cost, of low volatility, and that may be effectively employed at relatively low concentrations. It is a further object to provide an improved process for the fluorination of organic halides in the liquid phase by reaction with hydrogen fluoride, wherein the hydrogen fluoride may be employed in either concentrated or dilute form. It is a still further object to provide a multi-step fluorination process comprising both a vapor phase and a liquid phase reaction wherein substantial improvements in the effective utilization of hydrogen fluoride reactant are achieved and the amount of hydrogen fluoride waste product is substantially reduced.